It is known to provide a watchcase with a valve.
Nevertheless, in existing designs, the purpose of the valve is to enable one either to inject a gas into the case in order to obtain therein a pressure greater than the ambient pressure, thus preventing penetration of water, vapour or dust to the interior of the case or, to the contrary, establish a vacuum within the case in order to protect the movement from the effects of air contained in the case at the time of its closure, or with the purpose of improving the tightness of the case by the ambient pressure contributing to force the different constitutive elements thereof against one another.
Nevertheless, such designs have never been employed in order to eliminate effects on the watchcase of a long immobilization of the latter in a gaseous medium under heavy pressure.
Effectively, it has been determined that whatever be the sealing qualities of watchcases provided up to the present, when they are subjected during relatively long periods on the order of several hundreds of hours to relatively heavy pressure on the order of several tens of atmospheres and especially when the surrounding atmosphere is formed of a gas having small dimension molecules as is the case with helium for instance which is frequently employed in diving bells, the pressure within the watchcase ends up by increasing considerably.
Such conditions of use are not hypothetical but exist in reality, in particular when the watch is employed at great depths underseas in the course of work taking place under a bell. The dive is said to be "in saturation" (reference to the standards annex of ISO standard 6425 for diver's watches).
During return of the watch into an atmosphere at normal pressure, and this in spite of the decompression stages which are necessary for the occupant of the bell, there arises an interior overpressure in the watchcase, which may bring about bursting of the latter, that is to say, ejection of the crystal in particular.
To overcome this difficulty, patent document CH-A-492 246 proposes a valve arranged in a manner to open automatically when the ambient pressure is lower than that prevailing within the case and to close in the inverse case in order to prevent that there occur within the case an interior over pressure susceptible to bring about deterioration of the case during intermittent employment of the watch in an over-pressurized gaseous medium and during passage of the watch from the over-pressurized medium to the medium at ordinary pressure.
Given that precautions are taken in order to avoid bursting of the watch during a return from great depths, but in a gaseous medium, the wearer of the watch may wish to employ the same watch for great depths, but in a liquid medium on such latter occasion. Now the design recommended by the cited document shows that the valve suffers from shortcomings if the high pressure is applied to the exterior of the watch. The 0 ring employed may roll out of its housing if a high pressure is applied onto the head of the valve. Otherwise, from the fact that the course of the valve is limited in the return direction, it is necessary to arrange the housing of the seal with great precision in order to assure good application of the latter onto the watchcase. Simply stated, it is not easy to design a valve opening easily when the interior pressure is greater than the ambient pressure and hermetically closing when the pressure is directed in the other sense. It may also be mentioned that the use of the timepiece in a liquid medium is much more frequent than utilization under a bell with a helium atmosphere. It is thus necessary that the valve guarantee a perfect sealing during submarine dives while assuring its role as safety valve if the timepiece is occasionally employed under a bell.